This invention relates to additives for aqueous lubricants. Many aqueous lubricants have been generally known which contain various emulsifiers and solubilizers, but because of poor bactericidal action these aqueous lubricants are susceptible to damage by bacteria and so their life is shortened.
In an attempt to solve the above problem, it has been proposed to add some piperazine compounds to lubricants.
For example, there have been known aqueous lubricants containing piperazines or alkylpiperazines (U.S. Pat. Nos. 3,089,854 and 3,260,669), aqueous lubricants containing N-aminoethylpiperazine (Japanese Patent Unexamined Publication No. 67792/83), aqueous lubricants containing 1,4-piperazine ethanol (U.S. Pat. No. 2,441,793), etc.
Furthermore, phosphate ester lubricants comprising a phosphate ester contain various piperazine compounds (including those which are represented by the general formula [I] referred to hereinafter) which are not aqueous lubricants.
However, these aqueous lubricants and phosphate ester lubricants have the problems that bactericidal effects are still not sufficient. They become high molecular substances with heat or the like during their use as agents to cause adherence to the lubricated part or change of properties such as the formation of insoluble substances. In addition, their properties of rust emulsifiability and solubilizability are not proofing.